''Fukuiraptor'' ("thief of Fukui") was a medium-sized

megaraptora Megaraptora is a clade of carnivorous Tetanurae, tetanuran theropod dinosaurs with controversial relations to other theropods. Its Derived (phylogenetics), derived members, the Megaraptoridae are noted for their elongated hand claws and proporti ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur of the Early Cretaceous

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

(either

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is precede ...

or Aptian) that lived in what is now Japan. ''Fukuiraptor'' is known from the

Kitadani Formation The Kitadani Formation ( ja, 北谷層 ''Kitadani-sō'') is a unit of Lower Cretaceous sedimentary rock which crops out near the city of Katsuyama in Fukui Prefecture, Japan, and it is the primary source of Cretaceous-aged non-marine vertebrate f ...

and possibly also the

Sebayashi Formation The Sebayashi Formation is a Barremian to Albian geologic formation in Japan.

Description and history

The

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

is a partial skeleton (designated FPDM-V97122) discovered in the Kitadani quarry near Katsuyama in the

Fukui prefecture is a prefecture of Japan located in the Chūbu region of Honshū. Fukui Prefecture has a population of 778,943 (1 June 2017) and has a geographic area of 4,190 km2 (1,617 sq mi). Fukui Prefecture borders Ishikawa Prefecture to the north, G ...

. It is thought that this specimen was not mature and an adult may have been larger. The remains of many other individuals have been found in the quarry, with numerous humeri, femurs, and teeth being assigned to this species. However, the other individuals recovered from the same locality are mostly juveniles that were smaller than the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

(Currie & Azuma, 2006), in the smallest case less than a quarter of the holotype's size. A tooth (NDC-P0001) discovered in a block of conglomerate from the

Sebayashi Formation The Sebayashi Formation is a Barremian to Albian geologic formation in Japan.

has been referred to ''Fukuiraptor'' as well. As indicated by its slender phalanges, ''Fukuiraptor'' was a relatively lightly built animal, regardless of its maturity. In 2010

Gregory Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...

gave a length of 5 meters (16 ft) and a weight of 300 kg (660 lbs). Molina-Pérez and Larramendi estimated a length of 4.3 meters (14.1 ft) and a weight of 590 kg (1,300 lbs) in 2016. The distinctive teeth of ''Fukuiraptor'' show similarities with both

carcharodontosaurids Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...

(being very compressed and blade-like, as well as having wrinkled enamel) and tyrannosaurids (having oblique blood grooves near the serrations). The holotype also had very large and flat manual unguals (hand claws), which played a role in its initial classification as a dromaeosaurid (as the hand claws were mistaken for foot claws) as well as its current classification as a megaraptoran.

Classification

Initially considered a member of the

Dromaeosauridae Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...

when first discovered, its initial describers considered it a

carnosaur Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gig ...

, related to ''

Allosaurus ''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch ( Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alludin ...

''. More recent studies consider it a megaraptoran, an enigmatic group which may have been part of the family

Neovenatoridae Neovenatoridae is a proposed clade of carcharodontosaurian dinosaurs uniting some primitive members of the group such as ''Neovenator'' with the Megaraptora, a group of theropods with controversial affinities. Other studies recover megaraptorans ...

. However, more recently, another analysis has proposed that all

ns are actually tyrannosauroids, which would reclassify ''Fukuiraptor'' as a

tyrannosauroid Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...

coelurosaur Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyran ...

. Recent cladistic analysis of the theropod ''

Gualicho ''Gualicho'' (named in reference to the gualichu) is a genus of theropod dinosaur. The type species is ''Gualicho shinyae''. It lived in what is now northern Patagonia, on what was then a South American island continent split off from the superco ...

'' has suggested that ''Fukuiraptor'' and other megaraptorans are either

allosauroid Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were among ...

s, or non-tyrannosauroid basal coelurosaurs. Below is a cladogram reconstructing the position of Fukuiraptor in the Megaraptora as per Delcourt and Grillo, 2018.

Palaeoecology

In the

, where fossils of ''Fukuiraptor'' have been recovered, fossils of other vertebrates have been preserved. Among the species that have been properly described and named are '' Fukuisaurus tetoriensis'', a styracostern ornithischian, '' Fukuititan nipponensis'', a

titanosauriform Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence ...

sauropod, '' Koshisaurus katsuyama'', a hadrosauroid ornithischian, '' Fukuivenator paradoxus'', a maniraptoriform

, and '' Fukuipteryx prima'', an

avialan Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...

as defined by the authors''.''

External links

Image of the holotype skeleton, published by the twitter account of Thomas Holtz
*

References

{{Taxonbar, from=Q132536 Early Cretaceous dinosaurs of Asia Extinct animals of Japan Fossils of Japan Megaraptorans Taxa named by Philip J. Currie Fossil taxa described in 2000 Aptian life Barremian life